U.S. Pat. No. 5,061,727, teaches the making of [R-(R*,R*)]-5-[2-[5-(3-chlorophenyl)-2-oxo-3-oxazolidinyl]propyl]-1,3-benz odioxole-2,2-dicarboxylic acid diethyl ester, an oil which must be purified by a lengthy chromatography. The purity of the diethyl ester oil obtained is approximately 95% by area.